It is known that certain hydrocarbon halides such as alkyl halides in combination with organoaluminum compounds initiate the polymerization of cationically polymerizable monomers, such as isobutylene, styrene, .alpha.-methylstyrene, etc. (see for example, U.S. Patent 3,694,377). It is also known that the hydrocarbon halide need not be a small molecule, but may be part of a polymer chain, such as exists in chlorobutyl rubber, chlorinated ethylene-propylene copolymer, PVC, neoprene, etc. (see for example, U.S. Patent 3,904,708).
Comprehensive studies of hydrocarbon halide (initiator)/hydrocarbon-aluminum (coinitiator) initiator systems have led to an increased understanding of the initiation process (see J. P. Kennedy, J. Org. Chem., Vol. 35 p. 532, 1970). The major conclusion drawn from these studies is that the aluminum compound interacts with the hydrocarbon halide to ionize the carbon-halogen bond. The carbenium ion thus generated initiates the polymerization process. The reaction is viewed as proceeding by the following scheme: ##STR1##
Thus the organohalide (RX) reacts with an alkylaluminum compound (R.sub.3 'Al) to ionize the carbon-halogen bond in the initiator (eq. 1). in the absence of monomer (M), the ioncounterion complex collapses via alkylation of R.sup..sym. with an anion (R'.sup..crclbar.) from the counterion. However, if monomer is present, cationic polymerization ensues and generates a macromolecular-carbenium ion/counterion complex (eq. 3). Subsequently, this complex collapses via alkylation as in eq. 2 to yield a polymer with R' terminal group (eq. 4).
Knowledge gained from model studies has been exploited in the synthesis of: (1) quartenary-carbon containing compounds via reaction of tertiary hydrocarbon halides with R.sub.3 Al (see J. P. Kennedy, J. Org. Chem., Vol. 35 p. 532, 1970); (2) graft and bigraft copolymers via utilization of active-chlorine-containing polymers as initiators (see J. P. Kennedy and R. R. Smith, Recent Advances in Polymer Blends, Grafts and Blocks, ed. L. H. Sperling, Plenum Press, New York, 1974, pp. 303-357), and (3) block copolymers via utilization of difunctional initiators (see J. P. Kennedy and E. Melby, J. Macromol. Sci., Chem. A9(5) p. 833, 1975). It can thus be seen that exploitation of the hydrocarbon halide/hydrocarbon aluminum reactions has been primarily directed towards a controlled initiation in carbenium ion polymerizations, and subsequently placing well defined head groups in polyolefin chains.
Although the model studies also provided an understanding of termination mechanisms, and showed that termination involved alkylation of the carbenium ion by an anion from the alkyl-aluminum counterion, utilization of the alkylative termination was greatly limited due to the unreactive saturated hydrocarbon groups formed. Outside of synthesis of quartenary carbon containing compounds, utilization of alkylative termination has been confined to alkylating active chlorine sites (tertiary or allylic) on PVC. Thus PVC was treated with R.sub.3 Al compounds to alkylate the active sites, giving the stronger carbon-carbon bonds. It was speculated, and later verified, that such treatment on PVC would enhance its thermal stability (see J. P. Kennedy and M. Ichikawa, Poly. Eng. and Sci., 14, p. 322, 1974).
Therefore, the utilization of alkyl halide or hydrocarbon halide/alkylaluminum or hydrocarbon aluminum reactions to generate organic compounds with versatile functional groups has been ignored.
The novelty of this invention is a generalized process to synthesize cyclopentadiene-functionalized molecules, and primarily, cyclopentadiene-functionalized polymers, via Lewis acid chemistry. The scope of functionalized polymers prepared by the process of this invention include polymers with cyclopentadiene pendant groups and polymers with cyclopentadiene terminal groups.
The prior art in the synthesis of polymers with pendant cyclopentadiene groups involved either copolymerizations with allyl-dicyclopentadiene compounds, with subsequent thermal cracking of the dicyclopentadiene pendant groups, or by reaction of alkali metal salts of cyclopentadiene with halogenomethylated polyethers (see U.S. Pat. No. 3,826,760). These processes are limited by the problems inherent in copolymerizations, e.g., blockiness, and the general detrimental effect bases have on chlorine-containing polymers.
The prior art in the synthesis of cyclopentadiene-end group polymers involves the capping of living anionic polymerization chains with fulvenes, subsequent reaction with an alcohol yielding polymers with cyclopentadiene terminus (see Japanese Pat. No. 100,492/73). The reaction was viewed as occurring by the following scheme, illustrated with butadiene monomer: ##STR2## This process is limited to monomers which will polymerize anionically e.g., conjugated dienes, styrene and its derivatives.